Radio-surgery is a medical procedure that allows non-invasive treatment of benign and malignant tumors. It is also known as stereotactic radiotherapy (SRS) when used to target lesions in the brain, and stereotactic body radiotherapy (SBRT) when used to target lesions in the body. In addition to cancer, it has also been shown to be beneficial for the treatment of some non-cancerous conditions, including functional disorders such as arteriovenous malformations (AVM's) and trigeminal neuralgia. It operates by directing highly focused beams of ionizing radiation (e.g., X-rays, gamma rays) with high precision. It was initially developed in 1951, and can be used to ablate, by means of a precise dosage of radiation, intracranial and extracranial tumors and other lesions that are inaccessible using ordinary surgery techniques. There are many nerve diseases for which conventional surgical treatment is difficult or inadvisable, or have deleterious consequences, such as damage to nearby arteries, nerves, and other vital structures.
A linear accelerator (LINAC) may be used to deliver radio-surgery. LINAC-based radio-surgery was pioneered at the University of Florida College of Medicine and introduced by Betti and Colombo in the mid-1980s. Modern LINACs optimized for radio-surgery applications include the Trilogy machine from Varian Medical Systems, and the Novalis Tx radiosurgery platform, produced by Varian and BrainLAB. These systems differ from the Gamma Knife in a variety of ways. The Gamma Knife produces gamma rays from the decay of Co-60 of an average energy of 1.25 MeV. A LINAC produces X-rays from the impact of accelerated electrons striking a metal target (usually tungsten). A LINAC therefore can generate any number of energy x-rays. The Gamma Knife has over 200 sources arrayed in the helmet to deliver a variety of treatment angles. On a LINAC, the gantry moves in space to change the delivery angle. Both can move the patient in space to also change the delivery point. Both systems preferably use a stereotactic frame to restrict the patient's movement, although a frame is not needed on the Varian Trilogy and the Novalis Tx radiosurgery platform. The Varian Trilogy can also be used with non-invasive immobilization devices coupled with real-time imaging to detect any patient motion during a treatment.
While the LINAC systems provide many advantages, they are much more complex to control. For example, as the gantry rotates about the patient, the jaws and leaves of the collimator must be varied, and the signals to the linear accelerator must be varied, to implement a desired radiation dosage plan. This complexity limits the ability to implement certain types of treatment plans.